This invention relates to safety analysis of a product or system. More particularly, it relates to a method for conducting an analysis of a product or a system to evaluate hazards to personnel and identify mitigating conditions that include safety instrumented systems that are needed to control or avoid such hazards. It is important that minimum reliability requirements be established for these safety instrumented control functions.
A variety of different processes have been used in the past to determine safety of various systems. These processes are often introduced after the occurrence of a catastrophic event or after the occurrence of a consistent series of events resulting in harm to personnel. The application of safety instrumented control systems requires a hazard and risk analysis to be conducted to derive the need for a safety instrumented control function with suitable safety integrity to reduce the likelihood of an unsafe event occurring.
Preliminary hazard assessment (PHA) had origins from a combination of industry hazard checklists that are generally standard checklists. These checklists required identification of inherent hazards, which a test applicant must address specifically in a subsequent review session. One of the shortcomings of this process involves the task of addressing the risk that was left to an applicant, however, in any style deemed appropriate to the applicant's knowledge. Thus, the documentation of the approach and the results greatly varied, and required additional time and resources to ensure completeness. Also, gathering information with respect to critical hazardous features and combinations depended on an initial reviewer's expertise. Moreover, gathering information with respect to critical hazardous features and combinations can often present conflicting results that vary greatly.
Hazard characterization and personal safety analysis involve examination of hazards associated with a job or a task. In this technique, workers are grouped so that risks and exposures experienced by any member of a group are representative of the group as a whole. Information about the nature of a workplace, equipment and materials used, and the tasks to be performed may be considered as the basis of this step.
In another approach, a preliminary assessment of hazards requires a minimal effort to identify the inventory of hazardous materials to perform an initial hazard categorization. Reviewing basic facility information on intended facility operations and using estimates of materials may lead to an acceptable assessment. Hazard characterization also uses information from existing hazard analysis documentation such as, for example, safety analysis reports, process hazard analysis, job safety analysis (JSA), and the job hazard analysis.
Hazards are identified and resultant risks are assessed by considering probability of occurrence and severity of consequence. System safety is part of the overall program risk management decision process. Severity is an assessment of the worst credible potential consequence, defined by degree of injury or property damage that could occur. For example, but not limited to, hazard severity may be categorized as: catastrophic, critical, marginal and negligible.
Factors for identification of hazards include, but are not limited to, for example, (a) identification of hazardous components, (b) identification of hazardous operating conditions, (c) safety related interface considerations, (d) environmental constraints including operating environments, (e) training and certification pertaining to hazardous and safety critical operations and maintenance of hazardous and safety critical systems, etc.
Hazardous operations review analysis is performed to evaluate activities for hazards or risks introduced into a system by operational and support procedures and also to evaluate the adequacy of operational and support procedures that are used to eliminate or control identified hazards or risks. Typically, hazards are identified and evaluated by considering such criteria as plan system configuration and state at each phase of an activity; facility interfaces; supporting tools including software controlled automatic test equipment, to name but a few. Human factor(s) may be considered as an element of the total system, receiving both inputs and initiating outputs during the conduct of the analysis.
Safety efforts related to the hazardous operations review process focus primarily on the safe operation of a system. This process focuses on the operational phase of the system with specific emphasis on single-point failures. This process is not easily implemented for multiple system and multiple point failures.
Therefore, a need for a structured, standardized and efficient methodology for conducting a thorough analysis of a single product or a complex system to evaluate risk(s) to personnel and equipment, and identify mitigating factors to reduce the identified risk(s) has presented itself.